1. Technical Field
This invention relates generally to the field of signal conveyance and, more particularly, to techniques for signal manipulation on transmission lines.
2. Description of Related Art
Due to high costs associated with drilling for hydrocarbons and extracting them from underground formations, efficiency in drilling operations is desirable to keep overall expenses down. Electronic equipment may be useful in drilling operations to accomplish many tasks, such as providing identification information about specific downhole components to surface equipment, performing downhole measurements, collecting downhole data, actuating tools, and other tasks.
Notwithstanding its utility in the drilling process, downhole has proven to be a rather hostile environment for electronic equipment. Temperatures downhole may reach excesses of 200° C. Shock and vibration along a tool string may knock circuitry out of place or damage it. A drilling mud with a high pH is often circulated through a tool string and returned to the surface. The drilling mud and other downhole fluids may also have a detrimental effect on electronic equipment downhole exposed to it.
In the art, a first group of attempts to protect downhole electronics comprises an apparatus with electronic circuitry in a sonde that is lowered into a borehole by a cable periodically throughout the drilling process. The sonde provides protection from downhole conditions to the electronic circuitry placed inside. Examples of this type of protection (among others) may be found in U.S. Pat. No. 3,973,131 to Malone, et al. and U.S. Pat. No. 2,991,364 to Goodman, which are herein incorporated by reference.
A second group comprises adapting downhole tools to accommodate and protect the electronic circuitry. In this manner the electronic circuitry may remain downhole during drilling operations. For example, U.S. Pat. No. 6,759,968 discloses the placement of an RFID device in an O-ring that fills a gap in a joint of two ends of pipe or well-casing. U.S. Pat. No. 4,884,071 to Howard discloses a downhole tool with Hall Effect coupling circuitry located between an outer sleeve and an inner sleeve that form a sealed cavity.
A need remains for improved signal communication, generation, conveyance, and manipulation techniques, particularly in drilling operations.